The present invention relates to means for vision inspection of dimensional characteristics and sorting out defective IC components, in particular the so-called Surface Mount Devices (hereinafter SMD) typically used for the assembly of integrated circuits on printed circuit boards (PCB),especially those known as "small outline", "very small outline", and "thin small outline". Manufacturers may use thousands of various sizes of SMD devices in automated production runs of electronic equipment. Typical SMD device measurement features and tolerances, as shown in FIGS. 1A, 1B, 1C, and 1D, must be checked and sorted prior to their use. As a response to this need, vision inspection/sorting systems for screening IC devices for lead dimensions against predetermined measurements and tolerances were developed such as that described in several patents owned by the assignee of the present invention and listed in the table below disclosing apparatus and method for determining lead integrity of IC DEVICES, and are incorporated herein by reference in their entirety.
Linker, Jr. APPARATUS AND METHOD FOR LEAD INTEGRITY DETERMINATION FOR SMD DEVICES U.S. Pat. No. 4,686,637 issued Aug. 11, 1987 PA0 Linker, Sr. APPARATUS AND METHOD FOR LEAD INTEGRITY DETERMINATION FOR SMD DEVICES U.S. Pat. No. 4,704,700 issued Nov. 3, 1987 PA0 Linker, Sr. COPLANARITY INSPECTION MACHINE U.S. Pat. No. 5,045,710 issued Sep. 3, 1991 PA0 Linker, Sr. et al. LEAD INSPECTION AND STRAIGHTENING APPARATUS AND METHOD WITH SCANNING U.S. Pat. No. 5,146,101 issued Sep. 8, 1992
In these apparatus, the IC devices are usually gravity fed along an elongated trackway through several stations, and rely on a pin to pin scanning technique to determine IC device lead dimensional and coplanarity integrity. Generally, these apparatus include a first station for lead to lead scanning, a second station for lead coplanarity scanning, a third station for lead to lead straightening, and a fourth station for coplanarity adjustments. Lead to lead and coplanarity checks are performed by a sensor comprising a photodiode, prism, and a photodetector. A scanning means is moved axially along the length of the IC device to provide a signal upon intersection of each lead. Comparison of the signal with a predetermined signal determines the existence and spacing of each lead so that an accept, repair, or reject signal can be generated.
One device presently known for determining lead integrity provides a set of two photosensitive devices aligned one over the other on an axis parallel to the axis of the IC leads which are in proper, substantially parallel mutual relationship. IC leads are caused to intercept a light beam directed at the photosensitive devices by driving IC devices past the photo sensors through the use of motor driven belt arrangement. Thus, as the leads pass in proximity to the photosensitive devices, if the light of one of the photosensitive devices is blocked while the other continues to receive light, there is an indication that the IC lead is bent. The difficulty of such a system is that the motor and belts must be carefully regulated to maintain a constant speed while scanning occurs. Failure to maintain constant speed can result in false deviation determination. Consequently, IC devices that could be used will be rejected and discarded, which indicates the inefficiencies of such prior apparatus
A further known type of apparatus for determining the alignment of IC leads on a body is described in U.S. Pat. No. 4,553,843 "Apparatus For Determining the Alignment of Leads On A Body" wherein device leads are made to move axially between a light beam emitter and detector thereby generating signals which provide output data having information of the parallel bending of device leads.
Yet another apparatus described in U.S. Pat. No. 4,264,202 "Pin Receptacle Inspection Apparatus and Method" uses a collimated light source and a series of mirrors to reflect the light beam off pin receptacles. The reflected light is received by a photodetector which generates an output signal for determining when a predetermined bending threshold has been exceeded. Another apparatus using reflected light for lead inspection is U.S. Pat. No. 5,212,390. In addition to the above patents, apparatus currently commercially marketed by, for instance, Microvision, Texas Instruments, and Q-TEC employ three or four cameras to inspect device leads.
Thus, none of the aforementioned apparatus can inspect all device lead dimensions and characteristics simultaneously and ensure lead integrity in all situations. Further, prior art machines that are dedicated to the specific task of IC device integrity require movable scanning heads or photo emitters and receivers to measure and inspect IC leads. Image based systems such as those cited above, which use multiple cameras, are relatively slow, are costly to implement, and require large capacity computer storage and vision processing power to inspect and check device leads resulting in much slower throughput times and higher overall costs.
Accordingly, it is an object of this invention to provide an inspection means that allows simultaneous checking of IC device lead dimensions, characteristics, and markings with a single imaging means.
Yet another object of this invention is to provide an inspection means that allows inspection of all sizes (body widths and thickness, lead number, lengths, pitch, etc.) of IC devices.
A further object of this invention is to provide an inspection means that significantly increases inspection speed and throughput.
A still further object of this invention is to provide an inspection means that allows continuous feed through of IC devices.
It is another object of this invention to provide an inspection means that allows automatic sorting of defective IC devices without interruption of throughput speed.